The last & only ebike I had (a Packster 80) had a derailleur on it. I don't recall issues with shifting, aside from the standard ones (I hate not being able to shift while stopped).
On the other hand, I've had a Nuvinci N360 since 2012 on the non-electric cargo bike, and it's great. Now that I've added e-assist, though, it sucks. It's really really hard to shift under load. I end up just adjusting the motor assistance up and down rather than the gearing, because it's so annoying.
